Thin film heads having solenoid coils

ABSTRACT

A low-noise toroidal thin film head (&#34;TFH&#34;) device has low coil resistance and inductance, especially suitable for very high magnetic recording areal densities and channel frequencies. The length of a toroidal coil turn is only about 20-30% that of the length of an average turn in the conventional planar spiral coil design. This allows either reduction of the device thermal noise (by about 6 dB) and/or increase of the device operational frequency bandwidth (by a factor of 3-5). The toroidal coil coupling efficiency between each turn and the magnetic core is practically 100%, thereby improving the write and read-back efficiencies. In one embodiment a non-via large back-closure contact area is provided between the bottom and top magnetic poles along their entire back-side width, and all other open branches and loose ends in the magnetic circuit are eliminated. The magnetic core has a gradual, smooth toroidal (or a horse-shoe) shape with no loose ends, nooks, crevices, or sharp corners. The larger back-closure contact area decreases the magnetic core reluctance and improves the device efficiency. Utilization of a soft non-magnetic seed-layer, such as gold, eliminates interference noise due to the conventional magnetic (NiFe) seed-layer. Slight mechanical texturing (scratching) of the seed-layer along the intended easy axis helps to define and induce strong magnetic uniaxial anisotropy in the plated magnetic poles. All these features facilitate significant reduction of Barkhausen and other sources of device noise. Embodiments include conventional TFH&#39;s, Planar TFH&#39;s, Pinched-Gap TFH&#39;s, and various versions of Magnetoresistive (MR) TFH&#39;s.

This application is a continuation of application Ser. No. 08/727,694filed Oct. 7, 1996 which is now U.S. Pat. No. 5,703,740 which, itself,is a continuation-in-part of application Ser. No. 08/519,144 filed Aug.24, 1995, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to magnetic thin film heads (TFH) for recordingand reading magnetic transitions on a moving magnetic medium. Inparticular, the invention relates to a low-noise toroidal TFH devicehaving low coil resistance and inductance, especially suitable for veryhigh magnetic recording areal densities and channel frequencies. It isapplicable to both conventional and planar inductive and tomagnetoresistive (MR) heads using toroidal inductive write elements.

2. Background of the Prior Art

Magnetic TFH transducers are known in the prior art. See, e.g. U.S. Pat.Nos. 4,016,601; 4,190,872; 4,652,954; 4,791,719 for inductive devicesand U.S. Pat. Nos. 4,190,871 and 4,315,291 for magnetoresistive (MR)devices.

In the operation of a typical inductive TFH device, a moving magneticstorage medium is placed near the exposed pole-tips of the TFHtransducer. During the read operation, the changing magnetic flux frommagnetized regions in the moving storage medium induces a changingmagnetic flux in the pole-tips and the gap between them. The magneticflux is carried through the pole-tips and yoke-shaped core and aroundspiraling conductor coil winding turns located between the yoke arms.The changing magnetic flux induces an electrical voltage across theconductor coil. The electrical voltage is representative of the magneticpattern stored on the moving magnetic storage medium. During the writeoperation, an electrical current is caused to flow through the conductorcoil. The current in the coil induces a magnetic field across the gapbetween the pole-tips. A fringe field extends into the nearby movingmagnetic storage medium, inducing (or writing) a magnetic domain (in thestorage medium) in the same direction. Impressing current pulses ofalternating polarity across the coil causes the writing of magneticdomains of alternating polarity in the storage medium.

Magnetoresistive (MR) TFH elements can only operate in the read mode.The electrical resistance of an MR element varies with the direction ofits magnetization orientation. Magnetic flux from the moving magneticstorage medium induces changes in this orientation. As a result, theresistance of the MR element to a sensing electric current changesaccordingly. The varying voltage signal is representative of themagneatic pattern stored on the magnetic medium. An inductive element,optimized for writing, is used to record transitions in the magneticmedium.

In the manufacture of conventional TFH transducers for magneticrecording, a large number of devices are fabricated simultaneously bydepositing and patterning various layers on a ceramic wafer. Whencompleted, the wafer is cut (or diced) and machined into individualsliders each having at least one transducer. The main elements of a TFHinductive transducer, roughly in the order in which they are deposited,are the (alumina) undercoat, the bottom magnetic pole, the flux gapmaterial to provide spacing between the bottom and top magneticpole-tips, one or more levels of electrical conductive spiraling coilwindings interposed within insulation layers and located between theyoke arm parts of the bottom and top magnetic poles, the top magneticpole, elevated studs (or posts) for connecting the coil to bonding pads(above the overcoat), a thick (alumina) overcoat, and the bonding pads.In the case of an MR TFH device, the MR read element, along with itsshields, electrical leads, and biasing films (such as soft adjacentlayer and/or exchange bias layer) are usually fabricated prior to thefabrication of the inductive write element.

The prior-art design of an inductive TFH transducer includes top andbottom magnetic poles (layers), each comprising a pole-tip and a yokearm usually made of the alloy NiFe (permalloy). The magnetic poles areconnected through a back-via in the back side of one of the yoke arms.They are separated by a planar spiraling coil(s) and insulation layersin the yoke arm region, and by a thin gap layer between the pole-tips inthe front of the device. A typical prior-art TFH device is shown inFIGS. 1 and 2 of U.S. Pat. No. 4,190,872 (Feb. 26, 1980) to Jones et al,and in the front cover of Data Storage journal, the September 1994issue. The latter is a top-view color microphotograph of an actualprior-art TFH device. These figures illustrate some of the seriousdrawbacks of the prior-art TFH device. Since the back-via accommodatesonly a small fraction of the back-width of the yoke arms, it restrictsthe magnetic flux there, causing a full or a partial saturation (duringwrite operations), and thereby impairing the device efficiency andoverwrite capability. The magnetic layer inside the via consists ofmultiple domains in various orientations which are subject to extremelevels of stress and stress gradients. These increase the devicesusceptibility to magnetic noise, due to magnetic domain wall movements,through magnetostrictive interaction.

In addition, domain structure and orientation in the remaining backportions (to the sides of the via), as well as in the back-via itself,are ill-defined, raising the likelihood of Barkhausen, "popcorn", and/or"wiggle" noise occurrence. For example, the magnetic flux in the "wings"portions of the pole (at the back to the left and right of the via)during write operations, is normal to the hard-axis orientation of thepole layer. This results in domain wall movements during and after write(as well as read) operations. Such domain wall movements result inmagnetic noise. Often, the (top) magnetic layer is used for makingelectrical connections to other features, such as for electrical leadsconnecting the coil to the studs. An example of such electrical lead isclearly seen in the color photograph of Data storage (the gray permalloystrip from the coil via to the left side of the coil). This is similarto coil lead 21 in FIG. 1 of U.S. Pat. No. 4,190,872, which is oftenconstructed of plated permalloy (deposited during the plating of the toppole). Such portions of the magnetic circuit constitute open branchesand loose ends having undesirable magnetic domains, orientations, andcharacteristics. These domains may backlash and relax at different timesthan the main core, thereby adding to the total device noise.

Planar heads, or planar silicon heads (PSH), is another inductive TFHdesign in which the various layers, as well as the air bearing rails,are formed in a major plane of the substrate. Upon completion of thewafer fabrication, individual sliders are diced from the wafer withoutany further throat lapping, slider machining, or rail definition. Themagnetic core of the planar head has a general shape of a rectangularframe. The magnetic core frame includes an elongated bottom segmentformed at the plane of the substrate, two pillars (or studs) normal tothe bottom segment and connected to it on either side, and two topmagnetic pole-piece segments overlaying and parallel the bottom segment.The two top pole-piece segments are separated by a gap. Each of the toppole-piece segments is connected to one magnetic pillar on its sideopposite the gap. The top magnetic pole-piece segments includeadditional, narrower, pole-tips. These pole-tips are separated by amagnetic transducing gap. The transducing gap is thus located at the topof the magnetic core frame. The planar head further includes one or morelayers of spiral coils, which are wound around each of the magneticpillars.

The long planar spiral coil turns of the conventional TFH device (cf.FIG. 1 of U.S. Pat. No. 4,190,872 and the color photo of Data Storageand also FIG. 4(a) for a planar head and FIG. 5(a) for a conventionalTFH device with MR and a flat spiral coil) are inefficient in couplingthe magnetic flux in the core since they only wrap around a shortfraction or segment of the core length (around the back-via). Also, mostof each turn is located far from the magnetic core. According to apublication by N. Yeh in IEEE Trans. On Magnetics, Vol. MAG-18, No. 1,pp. 233-237, January 1982, the average turn efficiency is only about65%. Furthermore, the long turns have large resistance and parasiticinductance which limit the attainable device frequency and aggravatethermal noise. The large coil resistance generates excessive heat duringwrite operations. The excessive heat increases the device's Barkhausen,popcorn, and/or wiggle noise through magnetostrictive interaction of themagnetic core with thermal stresses. The latter are exerted by adjacentmaterials, having different thermal expansion coefficients, such asalumina and/or hard-baked insulation.

Another source for noise in the prior-art inductive TFH device is due tothe seed-layer used for plating the magnetic poles. The magneticproperties of the seed-layer are often quite different from those of theplated magnetic layers. In particular, the magnetic orientation,coercivity, and hard axis anisotropy field of the NiFe seed-layer may bequite different from that of the plated NiFe layers. As a result, thedifferent signal produced from the seed-layer (which is part of themagnetic core) is superimposed as a source of noise. Also, interfacialmechanical stress exerted between the seed-layer and the plated NiFemagnetic pole may contribute to the device's noise. Since the seed-layerusually consists of NiFe of somewhat different composition andmicrostructure than the plated alloy, the stress level and direction ofthe seed-layer can be different from that of the plated NiFe layers. Thedifferent stress may adversely affect the device noise throughmagnetostrictive interaction with the plated NiFe layers.

Prior art magnetoresistive heads use an inductive write element that is"merged" with the MR read element by sharing of a magnetic layer whichserves both as a top shield for the MR read element, and as the bottompole for the inductive write element. MR "combination" or "composite"heads comprise independent or separate MR shields and inductive writemagnetic poles. The flat spiral coil of the inductive write element hasa relatively small number of coil turns in order to reduce resistanceand inductance. The latter is required for high data transfer rates. Theoutput signal of an inductive head, when used in the read mode, isproportional to the number of coil turns. Therefore, the inductive writeelement of the MR head is inadequate for reading due to its relativelysmall number of turns. An MR head, combining an inductive write elementwith large number of turns but still having low inductance andresistance, will offer adequate read signal output, by the inductivewrite element, for servo pattern and/or data stored at large radiitracks on a spinning disk.

SUMMARY OF THE INVENTION

According to the present invention, the TFH device's magnetic noise issignificantly reduced by allowing the bottom and top magnetic poles tocontact each other along their entire back-side width (of the yokearms), and by eliminating all other open branches and loose ends in themagnetic circuit. The larger contact area between the poles at theirback-side also decreases the magnetic circuit reluctance, therebyimproving the device efficiency. In order to minimize the device noise,the ideal magnetic core should have a gradual, smooth toroidal (or ahorse-shoe) shape with no vias, loose ends, nooks, crevices, or sharpcorners. Also, no ferromagnetic material should be used for coil leads,or anywhere else, besides the magnetic core.

In another embodiment of the invention, a non-magnetic seed-layer(s)eliminates the noise contribution due to the commonly used magneticseed-layer. This seed-layer(s) must satisfy several requirements: Itmust be compatible for plating the (NiFe) magnetic layer upon it, itmust have good adhesion to the substrate, good electrical conductivity,and must not increase the corrosion susceptibility of the plated NiFepole-tips. For reducing stress related noise, the non-magneticseed-layer should consist of a mechanically soft metal or an alloy whichpossesses low internal stress to accommodate and absorb interfacial andinternal stresses of the plated NiFe layer. The preferred seed-layer isa combination comprising either Au over Cr adhesion layer (Au/Cr) or Auover Ti adhesion layer (Au/Ti). In addition, a type of mechanicallyinduced uniaxial magnetic anisotropy can be utilized to improveeasy-axis orientation of the magnetic poles. The seed-layer, or thesubstrate underneath, can be mechanically textured, for example, bylight scratching along the desired easy-axis direction, prior to platingthe NiFe magnetic poles. The scratching can be on an atomic scale (about5-50 Å deep), and can be readily produced on the soft metallicseed-layers, such as Au, Pd, or Pt, by brushing or wiping along thedesired direction. Alternatively, the mechanical texture can be producedon the substrate prior to the deposition of the magnetic poles (with orwithout a seed-layer).

In order to increase the read-back signal output, the read elementshould include the maximum possible number of coil winding turns. Theefficiency of each coil turn ought to be maximized. In accordance withthe present invention, the coil has a toroidal solenoid design. The coilwinding turns in this design are completely and closely wrapped aroundthe yoke arms (poles) over most of the core length, thereby ensuringeffective coupling with the magnetic core. All the coil turns of thesolenoid winding are situated along the width of the magnetic yoke arms,in a substantially normal direction to the direction of the magneticflux flow in the magnetic yoke arms during write and/or read operations.There is only one direction for he magnetic flux flow in each magneticpole: along the longitudinal, or hard axis of the yoke arm. In contrast,in the conventional spiral coil different portions of each turn inducemagnetic flux in different directions in the yoke arm. While the inducedflux direction in the front is along the longitudinal, or hard axis, theinduced magnetic flux in the "wings" portions of the yoke arm (on bothsides of the via) is along the transverse direction, or easy magneticaxis. The latter is a source of magnetic noise due to magneticdomain-wall movements. In the conventional spiral coil all windings arewrapped over a short segment of the magnetic core (at the back-via).Also, only a small fraction of each turn length is wrapped around themagnetic core, while the rest of it contributes to parasitic leakageinductance. As a result, the spiral coil does not couple effectively thecoil turns to the magnetic core. While the efficiency of each turn inthe toroidal solenoid coil is close to 100%, it is only about 45-75% inthe conventional planar spiral coil design.

The coil resistance and inductance are very important factors forlow-noise and high frequency device performance. They ought to beminimized in order to reduce the device thermal noise and improve highfrequency channel operation. The toroidal solenoid coil of the inventionfacilitates a much lower resistance, by a nominal factor of about 6,compared with the resistance of the conventional planar spiral coil.Decreasing the coil resistance by this factor facilitates reduction ofthe head thermal noise by a factor of about 2.45. This corresponds to animprovement of the thermal signal to noise ratio (SNR) by 7.8 dB!Alternatively, by maintaining the same thermal noise level as in theconventional spiral coil TFH design, the feasible bandwidth of thetoroidal TFH device can be increased by a factor of about 6! Loweringthe total coil inductance and capacitance can also expand theoperational device frequency. The toroidal solenoid coil significantlyreduces the capacitance and the parasitic coil inductance, andassociated noise of the spiral coil while significantly decreasingmagnetic flux leakage between the yoke arms. An unanticipatedcharacteristic of the toroidal head is the greatly reduced noise at highfrequencies compared to conventional thin film heads. Noise is reducedby a significant factor. Using this design, it is possible to increasethe read-back signal output while lowering the total coil resistance,reducing device noise, and increasing the channel frequency. Reducedpermeability roll-off at high frequencies, and faster flux rise in thepoles upon write current reversals, are other advantages of the toroidalTFH design over the spiral coil TFH. In the toroidal coil design themagnetic flux penetrates and propagates from both sides of each poleupon current reversals. In contrast, in the spiral coil design the coilturns are placed on one side only of each poles. As a result, the fluxpenetrates and propagates each pole from one side only in that design.The faster rise of the flux in the poles of the toroidal TFH producessharper write transitions. The reduced permeability degradation at highfrequencies improves the head efficiency at high frequencies and maypostpone the need for lamination of the poles. These advantagesfacilitate higher recording densities and higher data rate frequencies.

The toroidal TFH device occupies significantly smaller area (orfoot-print) on the slider than the conventional inductive or MR TFHdevices. This is due to the much smaller toroidal solenoid coil,compared with the conventional spiral coil. As a result, it is morefeasible and easier to fit a toroidal TFH device on small form-factorsliders, such as 30% of the original IBM 3380 type slider, sometimesreferred to as a "pico-slider", or even smaller form-factors. Thesmaller form-factors offer lower manufacturing cost, since more devicescan be fabricated per wafer of a given size. For example, while onlyabout 8,000 devices of 50% form-factor ("nano-slider") can be fabricatedon a single 6" round wafer, more than 20,000 devices of 30% form-factorcan be fabricated on such a wafer. The small form-factor sliders may beparticularly important for small form-factor (such as 2.5", 1.8", and1.3") disk-drives. Also, due to their lower mass, the smallerform-factor sliders offer lower friction between the slider and thedisk, thereby improving the drive durability and reliability. Asdescribed below in more detail, the toroidal TFH device can be combinedin various ways with an MR read element. Such combinations may also bespecially important for the very small form-factor disk-drives, wherethe disk velocity relative to the head is rather low, thus necessitatingthe use of an MR read element. Due to its very small foot-print, theinductive toroidal TFH enables such combinations (with an MR element) onthe smaller slider form-factors.

According to the invention, a planar toroidal TFH is formed by utilizingsimilar materials, processes, and methods as for the usual toroidal TFH.The planar toroidal device is somewhat similar to the usual toroidal TFHdevice. The top magnetic pole is split into two symmetric magneticpole-piece segments separated in the center by a transducing magneticgap. Each of these pole-piece segments forms a magnetic closure with abottom magnetic segment on either of its sides opposite the magnetictransducing gap. In contrast to the usual toroidal TFH, the air bearingsurface (ABS) of the planar toroidal TFH is located at the top of thedevice. The bottom and the top portions of the toroidal solenoid coil,wrapped around at least one of the magnetic core segments, compriseelectrically conductive strips with terminal contact pads. The bottommagnetic layer segment has a rectangular shape. The pole-tips and thetransducing gap are raised over the top magnetic pole-pieces by aninsulative pedestal. In at preferred embodiment, the magnetic pillars ofthe prior art are eliminated altogether. The top magnetic pole-piecesform magnetic closures directly with the ends of the bottom magneticlayer segment. In another embodiment, the magnetic core of the planartoroidal TFH is similar to the core of the prior art planar TFH, withtwo magnetic pillars. The top pole-pieces have a yoke-arm shape, similarto the poles in the usual toroidal TFH. The pole-tips may consist of anadditional layer formed on top of the pole-pieces, or they may beintegral portions of the pole-pieces formed in a single layer.

The planar toroidal head is embedded in an insulation material. Uponcompletion of fabricating the top coil layer, excess insulation layer isdeposited over the entire wafer and devices. This layer is thenlapped-down to expose the pole-tips and thereby to define the airbearing surface (ABS). Slider rails are then formed in the ABS byphotolithographic definition and etching. This is done at the waferlevel, simultaneously for all the devices on the wafer. Finally,completed individual sliders are diced from the wafer, with no furtherrail machining and/or throat lapping. In another embodiment, the planartoroidal TFH is built in a cavity formed in a flat surface of thesubstrate. At the end of the construction of the device, the device isburied under, and the cavity is filled with ceramic material such as Al₂O₃, SiO₂, or SiO. The final lapping exposes the pole-tips, forms asmooth surface across the wafer, and adjusts the throat height of thehead to its final dimension. Flying rails or other ABS patterns are thenformed in the ceramic layer, before the sliders are cut apart from thewafer.

The inductive element in the prior art MR heads cannot be used forreading due to several reasons. The small number of turns implies toolow signal output since the latter is directly related to the number ofcoil turns. Also, the much wider bottom pole would pick up data fromadjacent tracks, as excessive noise. Finally, the storage medium layeroptimized for MR heads is thinner (or lower M_(r) T) than the mediaoptimized for inductive heads. This further reduces the signal outputread by the inductive element in the prior art MR heads. The use of thetoroidal design for the inductive write element of a magnetoresistive(MR) head enables much higher writing frequencies because of the reducedinductance and capacitance. The lower coil inductance and capacitancesignificantly increase the resonance frequency of the circuit. Inaddition, the number of turns may be increased so that the inductivewrite element may also be used for reading either servo track dataand/or user data. MR heads, which combine an inductive toroidal element,enable the reading of data stored at larger radii tracks, near theoutside diameter (OD), by the inductive toroidal element. The MR elementof such head combinations is used for reading the data stored at smallerradii tracks, near the inside diameter (ID). Such combinations,therefore, may take advantage of the optimized reading properties ofeach element.

In other embodiments of the invention, the inductive toroidal elementmay be combined with a pinched-gap TFH device. The pinched-gap TFHstructures and methods for its manufacture are described in pendingapplications Ser. Nos. 07/963,783, 08/315,810, and 08/477,011, and in apublication entitled "A Pinched-Gap Magnetic Recording Thin Film Head",Paper #233, The Electrochem. Soc. Conf., Oct. 10-15, 1993, and in the3rd Int. Symp. on Magnetic Materials, Processes and Devices, edited byL. T. Romankiw and D. A. Herman, The Electrochemical Society, NJ (1994),incorporated herein by reference.

While the prior art (see for example, U.S. Pat. No. 4,743,988 issued May10, 1988 on an application of Sato et al.) discloses in FIGS. 15 and 16a structure which may appear superficially to resemble that of thisinvention, at least in the cross section shown in FIG. 15, in realitythe top magnetic pole of the structure shown in FIG. 15 is a continuoussheet which forms the top magnetic pole of at least two thin film headdevices. Because the second pole piece is a continuous sheet a solenoidtype coil is precluded from being formed around this second magneticpole. To the contrary, applicants have invented a structure which allowsa solenoid type coil to be formed around both the first magnetic poleand the second magnetic pole thereby to enhance the coupling efficiencyof the coils to the pole pieces albeit at an increase in the number ofprocessing steps required to fabricate the thin film head of thisinvention. However, the increased efficiency achieved by the structureof this invention more than compensates for the added processcomplexity. By adding more turns as is done in this invention, moresignal is obtained from a given magnetic transition on a storage mediaand thus a stronger output signal is generated by the thin film head.For a given number of turns around two pole arms, the thin film headlength can be significantly reduced to approximately a little more thanone half of the length that would be required using a solenoid typewinding around only one pole piece or alternatively, if the thin filmhead length is not reduced, approximately double the number of coilwindings around the two pole pieces can be obtained therebyapproximately doubling the signal strength generated from the thin filmhead from a given media.

An added advantage of the structure disclosed in this invention is thatthe inductance associated with the solenoid wound coils is reducedcompared to the inductance associated with spiral wound flat coils.Consequently, the real resistance resulting from a phase shift in theinductive impedance at high frequencies is significantly reduced therebysignificantly reducing the noise sensitivity of this thin film headcompared to prior art thin film heads.

Accordingly, one object of the invention is to provide a novel toroidalTFH magnetic transducer device with significantly improved efficiencyand lower noise level, and which can operate at substantially higherfrequencies than existing transducer devices.

Another object of this invention is to provide a toroidal TFH devicewith fewer winding turns, significantly lower coil resistance,capacitance, and inductance, and which provides significantly improvedperformance over the state-of-the-art TFH devices.

A further object is to provide a toroidal TFH device that has a greatlyreduced level of thermally generated electrical noise as compared tostate-of-the-art devices.

Another object of the invention is to provide a toroidal TFH device ofthe type described which has significantly improved frequency bandwidthfor writing and reading magnetic data.

A further object is to provide a toroidal TFH device of the typedescribed with substantially lower Barkhausen, popcorn, and/or wigglenoise by providing a full-width contact in the back-closure of themagnetic poles.

Another object is to provide a toroidal TFH device of the type describedwith substantially lower Barkhausen, popcorn, and/or wiggle noise byeliminating all open branches, nooks, crevices, and sharp corners in themagnetic core.

An additional object is to provide a toroidal TFH device of the typedescribed with substantially lower Barkhausen, popcorn, and/or wigglenoise than prior art transducers by providing a mechanically softnon-magnetic seed-layer(s) for plating the magnetic poles.

Yet another object is to provide a toroidal TFH device of the typedescribed with improved uniaxial magnetic anisotropy by using mechanicaltexturing of the seed-layer and/or the substrate prior to the depositionof the magnetic poles.

An additional object is to provide an improved TFH, combining aninductive toroidal write element and a magnetoresistive element, whichwill operate at much higher frequencies than conventional spiral coilinductive element, and which additionally is capable of reading servotrack and/or user data.

These and other objects and advantages of the present invention will nodoubt become apparent to those skilled in the art after having read thefollowing detailed description of the preferred embodiments which areillustrated in the several figures of the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective schematic view illustrating the principalcomponents of the TFH device according to this invention.

FIG. 1B shows a cross-section detail of the back-closure region of theembodiment of FIG. 1A.

FIG. 2 is a schematically illustrated longitudinal cross-section view ofa TFH device according to a preferred embodiment of the invention andimplementing the model of FIG. 1A.

FIGS. 3(a)-3(d) are plan views illustrating various stages during thefabrication of the TFH device of FIG. 2.

FIG. 4(a) is a schematic perspective drawing of a prior art conventionalplanar head.

FIG. 4(b) is a schematic longitudinal cross-sectional view of a planarTFH device structure according to one embodiment of the invention.

FIGS. 5(a) and 5(b) are schematic perspective and cross-sectional views,respectively, of a prior art "merged" magnetoresistive head.

FIGS. 6(a) and 6(b) are schematic perspective and cross-sectional views,respectively, of a toroidal TFH device in a "merged" magnetoresistivehead, according to one embodiment of the invention.

FIGS. 7(a) and 7(b) are schematic cross-sectional and perspective views,respectively, of a toroidal TFH device in a "merged" magnetoresistivehead, according to another embodiment of the invention, whichfacilitates the reading of servo and/or data by the inductive toroidalelement.

FIG. 8 is a schematic cross-sectional view of a toroidal TFH device in a"combination" magnetoresistive head, according to another embodiment ofthe invention, which facilitates the reading of servo and/or data by theinductive toroidal element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a schematic perspective view showing at 10 the principalcomponents of a TFH device according to the present invention. Thedrawing is not to scale. Each magnetic pole 12, 14 comprises arelatively large yoke arm 20, 28 and a relatively small pole-tip 22, 30.The bottom yoke arm 20 includes an elongated back portion 23 extendingbetween onset point 20B and back-end 26B of essentially constant width,and a fan-like front transition portion 21 of increasing widthcommencing at pole-tip 22 and extending between 20A and onset point 20B.Top yoke arm 28 has essentially the same shape as bottom yoke arm 20when viewed from the top. The indicated location of the air bearingsurface (ABS) corresponds to a slider body, in accordance with theconventional art thin film heads.

In another embodiment, the essentially constant width back portion ofthe pole is replaced with other, non-constant width shapes (not shown),such as a tapered width from a wider back-end to a narrower onset point.The taper angle of the tapered back portion of the pole of suchembodiment would not exceed the angle α of the fan-like transitionregion 21. The bottom magnetic yoke arm 20 and the top magnetic yoke arm28 contact each other, along substantially their entire width, at theback-closure region 26. The meaning here of "contact each other, alongsubstantially their entire width" means intimate magnetic, physicalcontact along at least 90%, and preferably along at least 95%, of thewidth of the back-ends of the yoke arms. Back-closure region 26 is shownin more detail in FIG. 1B and consists of a large contact area 26Dbetween the yoke arms with smooth and clean features. The back-closureregion does not include a via or any sharp steps, corners, loose ends,crevices, or nooks. This results in significantly reduced Barkhausen,popcorn, and/or wiggle noise, and elimination of any flux constrictionthere. In order to ensure sufficient contact area, the back closureregion length (equal to the distance between point 26A, the inner-mostpoint of contact between the yoke arms 20, 28, and the back-end 26B ofbottom pole 12, the outer-most contact between the poles) should be atleast equal to the thickness (T1 or T2) of the thinner of the yokes 20,28. Preferably, this distance should be between 1.2-2.0 times thethickness of the thinner of the yoke arms 20, 28. Back-ends 26B and 26Cmay terminate along the same line. However, due to natural processvariations of misregistration or misalignment, back-end 26C might beshorter than 26B (to the left of 26B in FIG. 1B, resulting inundesirable sharp step corners. In order to prevent such a situation,back-end 26C of top yoke arm 28 should preferably be slightly longer,i.e. extend to the right of 26B in FIG. 1B, and wrap around back-end 26Bof bottom yoke arm 20. Preferably, the distance between 26B and 26Cshould not exceed the thickness of top yoke arm 28. This lastrequirement is well within the capability of conventionalphotolithography. The larger back-closure contact area of thisembodiment decreases the core reluctance, thereby improving the deviceefficiency and overwrite capability.

Also illustrated in FIG. 1A are serially connected windings 32 and 36which are schematically shown wound about the yoke arms 20 and 28,respectively.

Coils 32 and 36 are shown as heavy lines in order to illustrate themanner in which they are wound around the bottom and top magnetic polesin a toroidal solenoid style. A toroidal solenoid coil differssignificantly from a flat spiral coil (sometimes called a "pancakecoil"). The toroidal solenoid coil is wound essentially like a helix(i.e. the coil resembles the threads of a screw) except due tolimitations of the manufacturing process, a cross-section perpendicularto the longitudinal axis of the solenoid coil is rectangular rather thanround. In this manner, the winding covers a substantial length of themagnetic core, thereby improving the coupling efficiency of each turn.The coil winding turns in the toroidal solenoid are completely andclosely (or tightly) wrapped around the poles 12, 14 over most of thecore length, thereby ensuring effective coupling with the magnetic core.All the coil turns of the solenoid winding are situated along the yokearms, producing substantially a single direction of magnetic flux flowin each magnetic pole along the longitudinal or hard axis direction,during write operations. During read operations the flux directioninduced in the core by the stored magnetic data in the storage medium isstill in a single direction (along the core's hard axis) at any point intime.

In contrast, in the conventional planar spiral coil, such as thatdisclosed in U.S. Pat. No. 4,190,872, different portions of each turninduce magnetic flux of different directions in different portions ofeach yoke arm. While the induced flux direction in the front portion isalong the longitudinal, or hard axis, the induced magnetic flux in the"wings" portions of the yoke arm (on both sides of the via) is along thetransverse direction, or easy magnetic axis. The latter is a source ofmagnetic noise due to magnetic domain-wall movements. All the turns ofthe spiral coil are wrapped over a short length of the magnetic core (atthe back-via) thereby impairing the effective coupling between the coiland the magnetic core. Also, only a small fraction of the length of eachturn in the conventional spiral coil is wrapped close to the magneticcore, while the rest of it is located far from the core. Since for eachwire segment the induced magnetic field strength is inverselyproportional to the distance from the wire segment, most of the spiralcoil wire contributes little to the core field during write operations.Similarly, much of the spiral coil contributes little to the inducedvoltage during read operations, but adds a significant parasitic leakageinductance and capacitance. As a result, the spiral coil does not coupleeffectively the coil turns to the magnetic core. While the efficiency ofeach turn in the toroidal solenoid coil is essentially close to 100%, itis only about 45-75% in the conventional planar spiral coil.

The toroidal coil of the present invention can achieve the sameread-back signal output level as the spiral coil, using only about 2/3the number of winding turns. The coil resistance, capacitance, andinductance are very important factors for low-noise and high frequencydevice performance. They ought to be minimized in order to reduce theTFH device thermal noise and improve high frequency channel operation.The length of each winding turn of the toroidal solenoid coil is shorterby a factor of about 3-5 compared with the average winding turn of theconventional spiral coil. Assuming the same number of turns and the samewinding cross-section, the toroidal solenoid coil has a lower totalresistance, by a factor of 3-5, compared with the conventional spiralcoil. However, less (about 2/3) turns of the toroidal solenoid coilproduce the same signal output as the conventional spiral coil. Forexample, a 30-turn toroidal solenoid coil produces essentially the sameoutput signal as produced by a 45-turn spiral coil. This allows evenlower total toroidal coil resistance, by a factor of about 4.5-7.5,compared with the conventional spiral coil. According to "The CompleteHandbook Of Magnetic Recording", 3rd edition by Finn Jorgensen, TabBooks, 1988, Page 232, the thermal resistance noise associated with thecoil is given by:

    V.sub.noise =(4kTBR).sup.1/2 volts

where k is the Boltzman constant (1.38×10⁻²³ J/°K), T is the temperaturein °Kelvin, B is the bandwidth in Hertz, and R is the resistance valuein Ohms. It is clear from this relationship that the higher the coilresistance and/or the higher the bandwidth, the noisier the device.Thus, decreasing the coil resistance by a nominal factor of 6, shouldfacilitate reduction of the thermal noise by a factor of 2.45. Thiscorresponds to an improvement of the thermal signal to noise ratio (SNR)of 7.8 dB! Alternatively, by maintaining the same thermal noise level asthe conventional spiral coil TFH design, the feasible bandwidth of thesolenoid coil TFH device can be increased by a factor of 6! It can thusdramatically reduce the device thermal noise at high frequencies.

The contribution of the head thermal noise is particularly important atvery high bandwidth frequencies. Lowering the total coil inductance L,and capacitance C, will also expand the operational device frequency,since the circuit resonance frequency is proportional to 1/(LC)^(1/2).The toroidal solenoid coil substantially eliminates the parasitic coilinductance and associated noise of the spiral coil. In addition, thelarge coil resistance of the conventional spiral coil generatesexcessive heat during write operations. The excessive heat in the priorart device increases the device's (Barkhausen, popcorn, and/or wiggle)noise through magnetostrictive interaction of the magnetic core withthermal stresses. The latter are exerted on the magnetic core byadjacent materials having different thermal expansion coefficients, suchas alumina or hard-baked insulation. In contrast, the low resistance ofthe toroidal solenoid coil of the present invention significantlyreduces such noise.

FIG. 2 (not to scale) is a longitudinal cross-section of a toroidal TFHdevice using thin film technology according to a preferred embodiment ofthe present invention. The device is fabricated over a suitablesubstrate 16 and highly polished undercoat 18. The substrate may becomprised of the usual Al₂ O₃ -TiC ceramic, glass, or other ceramicssuch as photoceram, calcium-titanate, or silicon carbide. Undercoatlayer 18 may be comprised of deposited Al₂ O₃, SiO₂, or SiO. Actualimplementation using thin film technology and fabrication proceduresincludes the step-by-step addition of magnetic core members andconductive strips which are ultimately interconnected to form themulti-planar equivalent of a solenoid coil helically wound about thecore members. The yoke arms 20, 28 are underlaid by a coil portion 32A,separated by coil portions 32B and 36A, and overlaid by coil portion 36Band insulation layers. On their front sides, the magnetic poles includethe bottom magnetic pole-tip 22 and the top magnetic pole-tip 30. Thepole-tips are separated by gap layer 24. Their throat height begins atthe zero throat point 30A, the inside point where the poles begin todiverge from each other, and terminates at the air bearing surface (ABS)of the slider, at the front of the device. The length of the throatheight is the distance between zero throat point 30A and the ABS. Theexact location of the ABS is determined by careful lapping of a sarfacecut perpendicular to the wafer's surface (following completion of thewafer fabrication), using auxiliary means, such as electric lappingguides (not shown). Along their length the pole-tips are separated by athin gap layer 24 that usually consists of sputtered alumina. In orderto provide intimate magnetic contact between the poles at back-closureregion 26, the gap layer 24 should be removed from that region prior tothe formation of top magnetic pole 14. This is further described below.

FIGS. 3(a)-3(d) are a series of schematic (not to scale) plan views ofvarious stages during the fabrication of the toroidal TFH deviceaccording to a preferred embodiment of the present invention. Since thinfilm technology does not permit the winding of a conductor about a polepiece, an analog of a conductive winding must be built up in stages suchas those depicted in the drawings. These stages relate to thefabrication of bottom pole 12 and solenoid coil 32 "wrapped" around it(cf. FIG. 1A). Similar stages are later utilized to fabricate top pole14 and its solenoid coil 36 (cf. FIG. 1A). To construct the lowerportion of winding 32, a pattern of elongated conductor bars 32A withenlarged staggering terminals or contact pads 32C are first formed inthe undercoat layer 18, as shown in FIG. 3(a). The conductor bars willconstitute the bottom half portion of the bottom pole's coil winding.The enlarged ends 32C of the conductor bars 32A provide terminals orcontact pads (allowing for adequate misalignment) for connection withthe conductors 32B (FIG. 2) of the top half portion of the bottom pole'scoil winding 32. The terminals are staggered in order to reduce thefeasible spacing between adjacent conductor turns. The conductors 32Aare comprised of a highly conductive metal such as Cu, Au, Pd, Pt, Ag,or Al. The metal strips can be electroplated or deposited by a dryvacuum method, such as evaporation or sputter deposition. In thepreferred embodiment, grooves having the pattern of FIG. 3(a) are firstetched into the alumina undercoat 18. The depth of the grooves isslightly over the required thickness of the coil conductors 32A (about3-5 μm). The grooves can be formed in undercoat 18 by the methoddescribed in U.S. Pat. No. 5,326,429 (Jul. 5, 1994) to Cohen et al,incorporated herein by reference. The same method can also be utilizedto form craters in undercoat layer 18 for other recessed features, suchas the bottom magnetic pole and other coil and insulation layers. Thismay be particularly important for improved planarization and polesymmetry of TFH devices with multi coil levels. The highly conductivecoil metal is then deposited onto the entire surface of layer 18 to fillthe grooves.

Next, the wafer is lapped to a flush flat surface, thereby removing themetal in all locations, except inside the grooves. A thin adhesion metal17 (in FIG. 2) is required under the highly conductive metal (except Al)in order to ensure adequate adhesion. The adhesion metal may consist ofCr, Ti, NiFe, Ta, Nb, Zr, W, Mo, and alloys comprising one or moreelements thereof. When the conductive metal is deposited by a dry vacuumtechnique, a thickness of about 100-300 Å of the adhesion metal issufficient. For a plated conductive metal, a seed-layer (17 in FIG. 2)with a thickness of about 500-2,000 Å is placed on the structure priorto plating. Other thicknesses for the seed layer can be used asappropriate. In the latter case, the seed-layer must have both goodelectrical conductivity and good adhesion to the alumina undercoat. Acombination of seed-layers such as Cu/Cr or Cu/Ti is quite common.

In an alternative embodiment, the conductive coil pattern of FIG. 3(a)can be constructed by a method described in U.S. Pat. No. 5,059,278(Oct. 22, 1991) to Cohen et al, incorporated herein by reference.According to that method, a selectively etchable seed-layer 17(consisting of a different metal than the conductive coil metal) isfirst deposited over the alumina undercoat. A photoresist plating mask,with openings having a pattern similar to FIG. 3(a), is then formed overthe seed-layer. The conductive metal coil is then plated through theplating mask. Finally, the photoresist mask is stripped off and theseed-layer is removed (from all other areas except under the coil) by aselective wet chemical etching which leaves the plated coil intact.Alternatively, the seed-layer 17 is etched non-selectively by a dry or awet etching technique.

Following the construction of the bottom portion of the bottom coil (32Ain FIG. 2), an insulative layer 19 (in FIG. 2) is deposited over theconductor bars 32A in order to insulate the latter from the magneticbottom pole 12. In the preferred embodiment, layer 19 consists of Al₂O₃, SiO₂, or SiO. Alternatively, layer 19 may consist of a patternedhard-baked photoresist, a regular polyimide, or a photosensitivepolyimide.

FIG. 3(b) shows the next stage, after depositing and forming the bottommagnetic pole 12 over insulative layer 19 (in FIG. 2). Magnetic pole 12may consist of the conventional NiFe alloy (permalloy) with acomposition of about 81-83% Ni and 17-19% Fe. It may also consist ofother ferromagnetic materials with large magnetic saturation (B_(s)) andpermeability (μ) and low coercivity (H_(c)) and anisotropy field(H_(k)). For low magnetic noise, the ferromagnetic pole material shouldpossess zero or low magnetostriction (λ_(s)). To enable high frequencyoperation of the device, eddy currents should be minimized in themagnetic poles. This can be accomplished by using a ferromagneticmaterial with poor electrical conductivity (insulators are the best) orby laminating metallic magnetic poles with non-magnetic insulatinglayers. Conventional permalloy and other alloys based on CoFe canconveniently be electroplated through a (photoresist) mask onto ametallic seed-layer. All ferromagnetic materials, including laminatedstructures which comprise alternating magnetic and non-magneticinsulating layers, can be deposited by dry methods such as sputtering.Desirable ferromagnetic materials may include NiFe, CoZr, CoNbZr,CoTaZr, FeSi, FeAlSi, FeN, FeAlN, FeTaN, CoFe, CoNiFe, CoFeB, and thelike. While electroplating is a more economical method (than the drytechniques) to form the magnet poles, it is limited to a few alloys andto a single layer. Laminating electroplated ferromagnetic alloys (withinsulating non-magnetic layers) requires extra steps for repeating theseed-layer, the plating mask, and the plating for each additionalferromagnetic layer. The dry techniques require shaping the magneticpoles after the deposition of the layer. This can be accomplished byion-milling, reactive ion etching (RIE), wet-etching, or a lift-offtechnique. The dry techniques offer the advantages of a wide variety ofmaterials and combinations, including laminations and high B_(s). Poleswith high magnetic saturation (B_(s)) are required to produce the highwrite-field required for good overwriting of high coercivity magneticmedia. The latter is required for high recording density. Laminatedstructures of alternating ferromagnetic and insulating layerssubstantially reduce degradation (or roll-off) of the permeability withfrequency, thereby substantially increasing the device operationalfrequency (or bandwidth). It appears certain that future fabrication ofTFH devices will include more dry processing of the magnetic poles.

In the conventional electroplating of the magnetic poles, a magneticmetallic seed-layer 12A (in FIG. 2) is first deposited over the wafersurface by sputtering or evaporation. This layer is required forelectrical continuity necessary for electroplating (the magnetic pole).A photoresist (frame) electroplating mask is then formed over theseed-layer. Next, the wafer is placed in an electroplating bath fromwhich the ferromagnetic pole is electrodeposited through the mask. Theplating mask is then removed, and the seed-layer, as well as platedferromagnetic layer everywhere except the magnetic pole, is removed bydry and/or wet etching. In one embodiment of the invention, anon-magnetic seed-layer(s) eliminates the noise contribution due to thecommonly used magnetic seed-layer. The seed-layer(s) must not increasethe corrosion susceptibility of the plated NiFe Layers when exposed tothe environment (the pole-tips in the air bearing surface). Theseed-layer(s) must also have adequate adhesion to the substrate, goodelectrical conductivity, and be compatible for plating the (NiFe)magnetic layer upon it. In order to reduce stress related noise, thenon-magnetic seed-layer should preferably consist of a mechanically softmetal or an alloy which possesses low internal stress. Such a seed-layercan accommodate and absorb interfacial and internal stresses of theplated NiFe layer. Examples of desirable seed-layers include a metalsuch as Au, Pd, Pt, Ag, and alloys comprising one or more elementsthereof, deposited over an adhesion layer selected from the groupconsisting of Cr, Ti, Ta, Nb, Zr, Mo, W, and alloys comprising one ormore elements thereof. Other seed-layers may include the group of Cd,In, Sn, Pb, and alloys comprising one or more elements thereof. Thelatter can be used as either a single seed-layer, or over an adhesionlayer selected from the group consisting of Cr, Ti, Ta, Nb, Zr, Mo, W,and alloys comprising one or more elements thereof. The preferredseed-layer is a combination comprising either Au over Cr adhesion layer(Au/Cr) or Au over Ti adhesion layer (Au/Ti).

Mechanically induced uniaxial magnetic anisotropy can be utilized inorder to improve easy-axis orientation of the magnetic poles. Forexample, the seed-layer, or the substrate underneath, can bemechanically textured, such as by light scratching along the desiredeasy-axis direction, prior to plating the NiFe magnetic poles. Theintended easy-axis, in the plane of the magnetic pole, should beparallel to the transverse or width direction of the yoke arm, andnormal to the hard-axis along the longitudinal or length direction ofthe yoke arm. The hard-axis of the yoke arm is the direction of themagnetic flux flow in the yoke arm during write and read operations,which is normal to the track direction (in the storage medium). Duringidle periods, most of the magnetic domains relax to orientations alongthe easy-axis. The scratching can be on an atomic scale (about 5-50 Ådeep), and can be readily produced on the soft metallic seed-layers,such as Au, Pd, Pt, Ag, Cd, In, Sn, or Pb by brushing or wiping alongthe desired direction. Similar mechanical texture can be produced onNiFe seed-layer also by brushing or wiping along the desired easy-axisdirection. Alternatively, the mechanical texture may be produced on thesubstrate prior to the deposition of the magnetic poles (with or withouta seed-layer). The latter may be particularly suitable for dry (orvacuum) deposition of the magnetic poles, which does not require anyseed-layer. In one embodiment, a soft Al layer is deposited andmechanically textured prior to a dry deposition of the magnetic pole(s).The soft Al layer absorbs or accommodates the interfacial stress of themagnetic layer. The mechanical magnetic anisotropy, thus introduced inthe magnetic poles, facilitates uniaxial easy-axis magnetic orientationalong the texture direction. The improved easy-axis orientation reducesundesirable domain walls and related noise in the device. In addition,the magnetic anisotropy introduced by the mechanical texturing maysignificantly assist to reduce, or completely eliminate, the presentlyrequired strong orienting magnetic field during the plating of NiFefilms. The orienting magnetic field is presently produced by a heavy,cumbersome, and expensive permanent magnet or an electromagnet. Thepresently required orienting field must be highly uniform and of severalthousand Oersteds strength. Such magnets or electromagnets are verycostly, particularly those designed for the larger wafer (6" diameter)plating cells.

As indicated above, FIG. 3(b) shows the shape of the bottom magneticpole 12 according to a preferred embodiment of the present invention.This pole consists of a yoke arm 20 and a pole-tip 22. The yoke armincludes an essentially constant width back portion 23 (between onsetpoint 20B and the back-end 26B). The yoke arm also includes a fan-like,neck, or transition front portion 21 between onset point 20B and point20A, the beginning of the pole-tip portion. For achieving the strongestpossible write-field, point 20A should coincide with zero-throat point(30A in FIG. 2), and the throat height should be less than the thicknessof the thinner of magnetic pole-tips 22, 30. This will ensure saturationof the pole-tips prior to any other location. However, sometimes it isdesirable to saturate the neck region prior to the pole-tips in order toprevent amplitude and resolution roll-off at excessively high writecurrents. In this case, it may be advantageous to retain in the neck aportion of the pole-tip to the left of 20A with the narrow constantwidth. Also, it may be quite difficult to align point 20A with the zerothroat point, particularly for the top magnetic pole with its hightopography, due to natural process deviations. For these reasons, asmall portion of the pole-tip to the left of 20A may be included in theneck region. Using thicker poles and/or pole materials having high B_(s)should also increase the feasible write-field. For a typical NiFe alloypole material, the thickness of the poles is in the range of 2-5 μm, andpreferably in the range of 3-4 μm. The length of the yoke arm portion 23between 20B and 26B (with constant width) ought to be minimized in orderto improve device efficiency and to reduce its inductance. However, thelength should be sufficient to accommodate all the coil turns andadequate spacings between them. Densely spaced turns may have a pitch ofabout 4.0-6.0 μm, with about equal width for the lines and spacings.Even more densely spaced turns will become feasible in the foreseeablefuture. In one example (described in more detail below), the bottom polemay have 16 toroidal solenoid turns, with line width of 3.0 μm andspacing width of 2.5 μm (or 5.5 μm pitch). The top pole may have 14turns of similar lines and spacings width. This will require a bottomyoke arm length of about 80-100 μm. Note, however, that although FIG.3(b) shows all the turns to be located between 20B and 26A, one or more(actually 3-4) turns can be placed in the fan-like front transitionregion 21 of the yoke arm in order to increase the number of turns andto improve efficiency. The width of the yoke arm back portion 23 betweenonset point 20B and back-end 26B should be optimized with regard toefficiency on one hand, and inductance and coil resistance on the other.The device efficiency improves with the width (increased cross-sectionfor the flux), but inductance and coil resistance also increase with thewidth. A desirable ratio between the width and the length of the yokearm is about 0.4-0.7, and more preferably 0.5-0.6. In the example, adesirable width of the yoke arm back portion 23 should be about 45-55μm. The angle α of the fan-like portion 21 of the yoke arm determinesthe length of this portion. While device efficiency increases with thisangle, so does the inductance and the magnetic (Barkhausen, popcorn,and/or wiggle) noise. A desirable value for α is between 30-60°, andpreferably 40-50°. The width of the pole-tips determines the writtentrack width (on the magnetic storage medium). The narrower thepole-tips, the narrower the tracks. However, the output signal isdirectly proportional to the width of the pole-tips. The currentstate-of-the-art width of the pole-tips is in the range of 3-5 μm. Muchnarrower pole-tips (and tracks), even below 1 μm, will become prevalentin the foreseeable future.

Following formation of the bottom magnetic pole 12, a non-magnetic gaplayer (24 in FIG. 2) is deposited over that pole. The purpose of thislayer is to create a magnetic transducing gap between pole-tips 22 and30 (in FIG. 2). The gap layer 24 usually consists of sputtered alumina.However, other non-magnetic materials, such as insulative SiO₂ or SiO,or even conductive or semiconductive materials can be utilized. Thethickness of the gap layer is optimized with regard to resolution (orlinear density along the track) on one hand, and overwrite andefficiency on the other. A thinner gap layer improves resolution (orlinear density) but degrades overwrite and efficiency. Thestate-of-the-art gap length (or gap thickness) is currently in the rangeof 0.2-0.4 μm, and is decreasing yet. It is likely that this thicknesswill be further reduced to 0.1-0.2 μm, or even less, in the foreseeablefuture. In order to provide intimate magnetic contact between the polesat back-closure region 26, gap layer 24 (in FIG. 2) should be removedfrom that region prior to the deposition of top magnetic pole 14. Thiscan be done by either a wet or by a dry etching (through a gap-etchmask) of the gap layer there. Removal of the gap layer at theback-closure region can be done at any stage following the gapdeposition but prior to the deposition of top pole 14. In the preferredembodiment, gap layer 24 is etched in the back-closure region 26 justprior to the deposition of top pole 14. This prevents contamination ofthe back-closure contact area during earlier processing steps of coiland insulation fabrication. For etching the gap at any stage, thegap-etch mask may consist of either photoresist alone or, preferably, aphotoresist on top of a thin metallic layer, such as NiFe or Cr. Thelatter technique is described in more detail in the first namedApplicant's Pending patent application Ser. No. 07/963,783 (filed onOct. 20, 1992), incorporated herein by reference. A wet gap etchant mayinclude hot phosphoric acid or, preferably, dilute (about 1:10) HF inwater. Dry etching can be accomplished by ion-milling, sputter-etching,or reactive ion etching (RIE). In the preferred embodiment, the gap-etchmask consists of a thin layer (100-300 Å) of NiFe with a photoresistlayer overlaying it. The wet chemical gap-etchant consist, of dilute(1:10) HF in water. This technique provides very high fidelitypattern-etching with virtually no undercutting, even with very longoveretch (up to 400%). The wet etching is isotropic, thereby ensuringcomplete removal of the gap layer from all hard to access locations,such as the step at back-end 26B.

FIG. 3(c) shows the stage after an insulation layer 25 has beendeposited and patterned over gap layer 24 and bottom magnetic pole 12(in FIG. 2). This layer consists of a hard-baked (cured) photoresist orpolyimide. The purpose of this layer is to increase the separation, andensure complete insulation, between magnetic pole 12 and its half topcoil portion 32B (cf. FIG. 2). Since the gap layer is rather thin, itmay not have complete step coverage over the edges of pole 12, thusresulting in electrical shorts between the coil and the core. Also, thevery thin gap may result in capacitive coupling between the two. In analternative embodiment of the invention, with adequate step coverage bygap layer 24, insulation layer 25 can be omitted altogether. Insulationlayer 25 is one of several insulation layers used in the devicefabrication. They all consist of either hard-baked photoresist orpolyimide and serve for insulation and/or planarization. The outer-mostinsulation layer defines the location of zero throat point 30A (cf. FIG.2). In the preferred embodiment, the outer-most insulation layer is thetop insulation layer 40 prior to the deposition of top pole 14. Itinsulates coil portion 36A from the top pole 14. This produces smoothslopes of top magnetic pole 14 at its front and back portions, withminimum or no bumps or mounds (cf. FIG. 2), thus reducing relatedBarkhausen, popcorn, and/or wiggle noise. However, the outer-mostinsulation layer can also be the bottom insulation layer 25 or anyinsulation layer therebetween. If layer 25 is the outer-most insulation,then its front end defines the location of zero throat point, and itsback-end can be used to define the front edge location 26A ofback-closure region 26. In the preferred embodiment, as shown in FIG.3(C), insulation layer 25 extends on the sides to a short distance fromthe coil contact pads 32C. These pads must remain exposed to facilitatecontacts with the top half portion of the bottom pole's coil. It is alsopossible to extend insulation layer 25 beyond pads 32C provided,however, that its pattern contains vias overlapping and exposing thecontact pads.

Vias, or a single wide opening on each side of the pole exposing thecontact terminals, must be formed in insulative layer 19 and gap layer24 over the contact pad terminals 32C (FIG. 3(a)) in order to facilitatecontacts between the bottom and top pad terminals of the bottom pole'scoil. In the case of layer 19 consisting of Al₂ O₃, SiO₂, or SiO, thevias can be photolithographically defined and etched at any stage priorto the formation of top half portion 32B (in FIG. 2) of the bottom coilbars. In one embodiment, the etching is done just prior to thedeposition of coil bars 32B. At this stage, gap layer 24 is already inplace, thus combining the pattern-etching of the two layers into asingle operation. In addition, the delayed etching preventscontamination of the vias during earlier processing steps. In the caseof insulative layer 19 consisting of hard-baked (fully cured)photoresist or polyimide, preferably the side borders of this layer aredefined by photolithography to extend to within a short distance fromthe contact pads. Alternatively, layer 19 extends beyond the contactpads, but vias exposing the latter are defined by photolithography priorto curing it.

FIG. 3(d) shows the stage after deposition and patterning of the tophalf portion 32B of the bottom pole's coil over insulation layer 25.Terminals or contact pads 32C in the conductor pattern allow thecompletion of the bottom pole's solenoid coil. Terminal or contact pad32D serves for connecting the bottom pole's solenoid coil with the toppole's solenoid coil after it is formed. Terminal 34 of the conductorpattern is one of the (two) coil leads. The other one, terminal 38, isshown in FIG. 1. The leads connect the coil to bonding studs or posts,or directly to the device bonding pads (not shown). The latter serve forwire bonding to an external read/write channel circuit. In the preferredembodiment, coil terminals 34 and 38 are located near the back of theTFH device. This facilitates efficient utilization of the real estatenear the device, and minimizes the leads resistance. In alternativeembodiments, the terminals can be located in the front of the device, orone in the front and the other one in the back of the device. Also, onlya single (either top or bottom) pole's solenoid coil may be chosen undercertain circumstances. This may be the case when an inductive writeelement is combined with an MR read element.

Another possibility is when one inductive element, optimized for writefunction, is combined with another inductive element, optimized for readfunction. Such an inductive write element may require less windingturns. A single pole's solenoid coil simplifies the device constructionin a very substantial way. In other alternatives, various combinationsof pole's windings are possible. For example, it is possible toconstruct more than a single level of winding on one or both poles. Itis also possible to have more levels of winding layers wrapped aroundone pole than on the other pole. Similarly, it is possible to constructsimilar number of winding levels on each pole, with equal or differentnumber of turns wrapped around each pole.

The top half portion 32B of the bottom pole's solenoid coil isfabricated in a similar way to the bottom half portion 32A of the coil.Similar conductor materials and fabrication techniques can be utilized.In the preferred embodiment, this layer is constructed by platingthrough a photoresist mask onto a selectively etchable seed-layer,utilizing the method of U.S. Pat. No. 5,059,278, as described above.Alternatively, coil layer 32B can be formed by dry techniques, or by theusual electroplating technique, as described above for coil layer 32A.FIG. 3(d) shows contact pad 32D to be located ahead of the other contactpads 32C. This is to emphasize that contact pad 32D is unique in that itprovides continuity contact to the top pole's coil 36A. In reality,however, this pad may also be located along the same line like the restof contact pads 32C.

The rest of the fabrication of the toroidal TFH device is similar tothat previously described and uses similar materials, patterns, andfabrication steps. For this reason, the remaining steps are mostlydescribed with reference to FIG. 2. Following the construction of coillayer 32B, one or more insulation layers consisting of hard-bakedphotoresist or polyimide, is deposited and patterned over coil layer32B. Usually, two insulating layers 37 and 38 are used prior to theconstruction of coil layer 36A. The first layer 37 is used to fill inthe spaces between coil turns 32B. The second insulation layer 38 isused to planarize the surface prior to the construction of coil layer36A, and to provide sufficient insulation between coil layers 32B and36A. However, a single, rather thick, insulation layer may be used forboth purposes. Similarly, one or more insulation layer(s) 40 aredeposited and patterned over coil layer 36A in order to fill in thespaces between its turns, planarize the surface, and insulate coil layer36A from the top magnetic yoke arm 28. The insulation layers between thebottom magnetic yoke arm 20 and the top magnetic yoke arm 28 arecollectively designated as "Insulation" in FIG. 2. They consist ofhard-baked (or cured) photoresist and/or cured polyimide. The latter mayconsist of a regular or a photosensitive polyimide. All the insulationlayers are patterned prior to curing. The curing of a hard-bakedphotoresist can be carried out by baking for several hours at atemperature ranging between 200-250° C., under vacuum or inertatmosphere. Hard-baking is often carried-out under external magneticfield to ensure proper orientation of the easy axis of the poles.Polyimide usually requires higher curing temperature. This may adverselyaffect the magnetic properties of the NiFe poles, which begin todeteriorate at temperatures above about 250° C. The contact pads of coillayers 36A and 36B can be placed beyond the sides borders (or extent) ofthe insulation layers, or within vias defined in the insulation layers.In the preferred embodiment, these pads are placed beyond the sideborders of the insulation. Although such placement increases slightlythe length (and resistance) of each turn, it simplifies the fabricationprocess by eliminating contact vias and the associated risk of poorelectrical contact due to contamination or insulation residues insidethem. Also in the preferred embodiment, all insulation layers followingthe construction of coil layer 32B are placed over and cover (orinsulate) contact pads 32C. They extend on both sides of the devicebeyond contact pads 32C, but do not cover contact pad 32D. The latterprovides a connection to the top pole's coil through the first (or last)contact pad of coil layer 36A. As described above, the outer-mostinsulation layer between yoke arms 20 and 28 defines zero throat point30A. In the preferred embodiment, the outer-most layer is the topinsulation layer 40 (under yoke arm 28). The outer-most layer can alsobe used to define the inner-most point 26A of the back-closure region26.

Construction of the bottom half portion of the top pole's coil layer 36Ais similar to the construction of coil layer 32B. In the preferredembodiment, the method of U.S. Pat. No. 5,059,278 is used to form thislayer. A selectively etchable seed-layer (not shown) is deposited overthe insulation layer 38. A plating photoresist mask (not shown) is thenformed over the seed-layer, and coil layer 36A (consisting of anothermetal than the seed-layer) is plated through the mask openings onto theseed-layer. The plating mask is then removed and the seed-layer isselectively etched from between the turns. The pattern of coil layer 36Aincludes contact pads which provide continuity to the bottom pole's coil(through pad 32D) and to the top half portion of the top pole's coillayer 36B. The contact pads' pattern is similar to that of coil layers32A and 32B. In general, the top pole's coil includes fewer turns thanthe bottom pole coil. The reason is that there is less space along thetop pole, as can be seen in FIG. 2. In the example discussed below, thebottom pole solenoid coil includes 16 turns while the top pole solenoidcoil includes 14 turns.

One or more insulation layer(s) 40 is now deposited and patterned overcoil layer 36A. Provisions are made to ensure that the contact padsconnecting to the top half portion of the coil are not blocked by thislayer. As described above, this can be best accomplished by not coveringthe contact pads by this insulation layer(s). This means that the sideborders of this insulation layer(s) only extend to within a shortdistance from the pads. Note, however, that at this stage continuitycontact between coil layers 32B and 36A has already been formed at pad32D. It is therefore desirable to cover this contact by the topinsulation layer. As described above, in the preferred embodiment thegap-etch operation to clear the back-closure region 26 is delayed untilthis stage. This ensures clean surface of this region prior to thedeposition of the top magnetic pole.

The top magnetic pole 14 can be constructed of similar materials, andformed in a similar way to those of bottom pole 12. Either the samemagnetic material or a different one than the bottom pole can be used.Like the bottom magnetic pole, the top magnetic pole can be laminatedfor improved high frequency response. The thickness of the magneticpoles may be the same or different from each other. In particular, polesconsisting of different magnetic materials may also have differentthickness. The shape of the top magnetic pole is essentially similar tothat of the bottom magnetic pole 12 (cf. FIG. 3(b)). The pole-tips mayhave different widths. In particular, it is a common practice to designa wider bottom pole-tip than the top pole-tip. It is also possible toconstruct one or more of the magnetic poles with wider pole-tip than itsfinal width, and then trim the pole-tip(s) to its final width. Suchpole-trimming is described for example in U.S. Pat. No. 5,141,623 (Aug.25, 1992) and U.S. Pat. No. 5,200,056 (Apr. 6, 1993) to Cohen et al,incorporated herein by reference. The topography of the top pole isusually worse than that of the bottom pole. Most of the top pole issituated at a higher elevation than the pole-tip. This may causeBarkhausen, popcorn, and/or wiggle noise due to uncompensated stresses,the presence of unfavorable domains, and domain pinning in the sloppingregions. Also, for a plated top magnetic pole, the unfavorabletopography of the top pole adversely affects its composition uniformityacross a device. Composition non-uniformity across a TFH device is knownto increase its noise. The top pole topography aggravates the differencein the plating mask aspect ratios between the back portion of the yokearm and the pole-tip region. This causes depletion of iron ions (theminor constituent in the NiFe plating bath) inside deep and narrowopenings (pole-tips), compared with wide and shallow openings in theyoke arm portions. The topography of the top pole can be improved (orplanarized) by embedding the bottom pole, as well as several coil andinsulation layers, in a recessed crater etched in the undercoat, asdescribed above (cf. U.S. Pat. No. 5,326,429).

Next, an insulation layer 41 is deposited over the top magnetic pole 14.In one embodiment, this layer consists of Al₂ O₃, SiO₂, or SiO. Thepurpose of layer 41 is to insulate top magnetic pole 14 from the coillayer 36B. It must have adequate step coverage over the sides of pole14. For this reason, the thickness of layer 41 ought to be at least 0.5μm, and preferably be in the range of 1.0-3.0 μm. Also in thisembodiment, layer 41 may extend over the entire length of the device;from the ABS to the back-end 26C, and beyond, as seen in FIG. 2.However, when layer 41 consists of Al₂ O₃, SiO₂, or SiO, it may exertstress on the top magnetic pole, thereby increasing the Barkhausen,popcorn, and/or wiggle noise. Also in this embodiment, vias must beetched in layer 41 in order to expose the underlying contact pads ofcoil layer 36A.

In an alternative embodiment, insulation layer 41 consists of ahard-baked photoresist or polyimide. These insulation materials aresofter and exert little or no stress on the top magnetic pole 14,thereby reducing the device's noise. In this embodiment, the insulationlayer is first deposited and patterned, prior to its curing. Theinsulation patterning leaves exposed the contact pads of coil layer 36A,as described above for coil layers 32B and 36A. Also in this embodiment,the insulation layer 41 does not extend in the front all the way to theABS, in order to avoid its smearing and/or cause degradation ofstructural integrity there. In this case, the insulation layer mayextend in the front up to the end of the top flat region, but not overthe front slopping region of the top pole. In the back of the device,this layer may extend all the way to back-end 26C, or beyond. Thehard-baked photoresist or polyimide insulation layer may extend on thesides of the device to within a short distance from the contact pads, asdescribed above for coil layer 36A.

Construction of the top half portion of the top pole's coil layer 36B issimilar to the construction of previous coil layers, such as 32B or 36A.Contact pads, similar to those of coil layer 32B should overlay thecontact pads of coil layer 36A. An electrical lead (38 in FIG. 1),similar to 34 in FIG. 3(d), but on the other side of the device, isprovided in the pattern of coil layer 36B. This lead connects the coilto the other terminal with a stud and/or bonding pad, where wire bondingconnects the device to the external channel circuit.

The final step in the wafer fabrication includes the deposition of anovercoat or an encapsulation layer (not shown) over the entire wafersurface. The overcoat layer may consist of Al₂ O₃, SiO₂, or SiO. In thepreferred embodiment, this layer consists of relatively thin (10-15 μm)Al₂ O₃, utilizing the studless method of U.S. Pat. No. 5,326,429. Thatmethod includes the formation of bonding pads over the coil terminals,followed by deposition of the overcoat and etching vias through it toexpose the bonding pads. Wire bonding to the bonding pads isaccomplished through the vias. Otherwise, thick studs are formed at thecoil lead terminals, followed by deposition of much thicker overcoat(35-60 μm), and back-lapping of the wafer to expose the studs. Bondingpads are then formed over the studs, thus completing the waferfabrication process.

EXAMPLE

A toroidal TFH device, in accordance with the invention, comprises NiFebottom and top magnetic poles with thickness of 3.5 μm, and constantyoke arm width of 50 μm. The length of the constant-width yoke armportion is 90 μm, and the length of the fan-like yoke arm portion is 22μm. The fan angle α is 45° (cf. FIG. 3(b)). The coil includes 30 turnsconsisting of 16 solenoid turns wrapped around the bottom pole, and 14solenoid turns wrapped around the top pole. Each turn having a width of3.0 μm and thickness of 3.0 μm (cross-section of 9.0 (μm)²). The averagelength of a turn is 2×70 μm (including both sides of the yoke arm). Thetotal coil resistance is given by the formula

    R=ρ(l/A)

where R is the total coil resistance (in Ohms), ρ is the resistivity ofthe coil material (in Ohm-cm), l is the length of the coil (in cm), andA is the average cross-section of a turn (in cm²). Using copper for thecoil with ρ=1.7×10⁻⁶ Ohm-cm, and substituting the coil values in theformula,

    R=1.7×10.sup.-6 (30×2×70×10.sup.-4)/(9×10.sup.-8)=7.93 Ohms.

For comparison, a conventional 30 turn spiral coil TFH device has coilresistance of about 35 Ohms. The resistance per turn of the toroidalsolenoid coil is only about 23% of the average spiral coil turn.Furthermore, the 30 turns of the toroidal TFH device produce the sameread-back signal output as a 45 turn spiral coil conventional head. Thelatter has a total coil resistance of about 52 Ohms! Thus, the 30 turntoroidal TFH device of the invention provides the same output signal asa 45 turn conventional spiral coil TFH device, but has only about 15% ofthe total coil resistance of the latter! The inductance L of anelectromagnetic solenoid element is given approximately by:

    L=N.sup.2 μA/l

where N is the number of coil turns, μ is the permeability, A is thecross-section area of the coil, and l is the length of the coil. Theinductance of the 30 turn toroidal TFH device is less than 44% of the 45turn conventional spiral coil TFH device, based on the number of coilturns alone. In addition, the spiral coil inductance is much larger(particularly at high frequencies, when μ of the core rolls-off) due toits larger cross-section A and its associated parasitic air inductance.Also, the capacitance of the spiral coil is larger due to the muchlonger turns which present enhanced capacitive coupling between theturns. Basically, the inductance of any coil is dominated by itscross-sectional area. Therefore, the conventional spiral design hasapproximately five to ten times higher inductance than the toroidaldesign, depending on the number of layers used in the spiral coillayout. Since the circuit resonance is proportional to (1/LC)^(1/2), thelower inductance and capacitance of the 30 turn toroidal headfacilitates at least 100% increase of the feasible bandwidth over theconventional 45 turn spiral coil device.

The toroidal TFH device occupies significantly smaller area orfoot-print on the slider than the conventional inductive or MR TFHdevices. This is due to the much smaller toroidal solenoid coil,compared with the conventional spiral coil. As a result, it is morefeasible and easier to fit a toroidal TFH device on small form-factorsliders, such as 30% of the original IBM 3380 type slider, sometimesreferred to as a "pico-slider", or even smaller form-factors. Thesmaller form-factors offer lower manufacturing cost, since more devicescan be fabricated per wafer of a given size. For example, while onlyabout 8,000 devices of 50% form-factor ("nano-slider") can be fabricatedon a single 6" round wafer, more than 20,000 devices of 30% form-factorcan be fabricated on such a wafer. The small form-factor sliders may beparticularly important for small form-factor (such as 2.5", 1.8", and1.3") disk-drives. Also, due to their lower mass, the smallerform-factor sliders offer lower friction between the slider and thedisk, thereby improving the drive durability and reliability. Asdescribed below, the toroidal TFH device can be combined in various wayswith an MR read element. Such combinations may also be speciallyimportant for the very small form-factor disk-drives, where the diskvelocity relative to the head is rather low, thus necessitating the useof an MR read element. Due to its very small foot-print, the inductivetoroidal TFH enables such combinations of an inductive coil with an MRelement on the smaller slider form-factors.

In a conventional TFH, the air bearing rails are defined in a cutsurface which is normal to the original wafer surface. This implies thatthe TFH device is fabricated over a major surface of the substrate,which in operation is normal to the magnetic storage medium. Suchconfiguration requires laborious machining and/or etching of the airbearing rails, as well as throat lapping, in the cut surface. Incontrast, planar thin film heads, such as planar silicon heads (PSH)devices, are fabricated along with the air bearing rails in a majorsurface of the wafer substrate. During read and write operations, themajor surface of the planar head is parallel to the surface of themagnetic storage medium. Upon completion of the wafer fabrication, theplanar head devices are diced from the wafer into complete sliders, withno necessity for further machining of the rails or throat lapping. Incontrast to conventional TFH sliders, where the active element is formedon the trailing edge of a rail, normal to the storage medium, the activeelement of the planar head is embedded at the bottom of the rail,parallel to the storage medium.

FIG. 4(a) shows a typical prior art planar head with two levels (2L) ofspiral coils. The magnetic core of the planar head has a general shapeof a rectangular frame. The magnetic core frame includes an elongatedbottom segment 20 formed at the major plane of the substrate, twopillars (or studs) 21A, 21B, normal to the bottom segment and connectedto it on either side, and two top magnetic pole-piece segments 28A and28B overlaying and parallel to the bottom segment 20. The two toppole-piece segments 28A, 28B are separated from each other by a gap 24.Each of the top pole-piece segments 28A, 28B is connected to onemagnetic pillar 21A, 21B, respectively, on its side opposite the gap 24.As shown in FIG. 4(a), each of the top magnetic pole-piece segments 28A,28B includes an additional, narrower, pole-tip 30A or 30B, respectively.The pole-tips 30A, 30B are separated by a magnetic transducing gap 24.The transducing gap 24 is thus located at the top of the magnetic coreframe. The planar head includes one or more layers of spiral coils, twoof which (22A, 22B) are shown, which are wound around each of themagnetic core pillars. Contacts to the spiral head coils 22A, 22B aremade through holes in the slider body.

FIG. 4(b) illustrates in cross-section an embodiment of the invention inwhich a toroidal TFH design is incorporated in a planar head. The planartoroidal TFH is formed on the substrate 16 by utilizing similarmaterials, processes, and methods as described above in conjunction withthe structure shown, for example, in FIG. 2 and related figures.Corresponding elements in FIG. 4(b) are labeled the same as in previousfigures. The planar toroidal TFH device of FIG. 4(b) is somewhat similarto the toroidal TFH device shown in FIG. 2. Here the top magnetic poleis split into two (symmetric) magnetic pole-piece segments 28A, 28Bseparated in the center by a transducing magnetic gap 24. Each of thetop magnetic pole-piece segments 28A, 28B forms a magnetic closure 27A,27B, respectively, with the bottom magnetic segment 20, on either of itssides and opposite the transducing magnetic gap 24. Note that the airbearing surface (ABS) is located at the top of the wafer as shown inFIG. 4(b). The bottom coil portion 32A, which forms a Toroid around thebottom magnetic segment 20, comprises electrically conductive stripswith enlarged terminal contact pads (not shown), fabricated in a mannersimilar to the manner in which the structure described in FIG. 3(a) isfabricated. Although the enlarged terminal contact pads may be omitted,the contact pads facilitate consistent contacts, even under naturalmisalignments and process deviations. At least one turn of a solenoidwinding is wrapped around at least one segment (such as segment 20) ofthe magnetic core. In the preferred embodiment, the bottom coilconductive strips 32A are embedded in insulation layer 18, as waspreviously described in FIG. 2. The latter may comprise Al₂ O₃, SiO₂, orSiO. Other steps of the head construction proceed in a manner similar tothose previously described. Bottom magnetic layer segment 20 may have arectangular shape, as shown for segment 20 in FIG. 4 (a). The pole-tips30A, 30B and the transducing gap 24 are raised over the top magneticpole-pieces 28A, 28B by a pedestal 44. Pedestal 44 may comprise aninsulation material such as hard-baked photoresist or cured polyimide.Alternatively, pedestal 44 may comprise a material such as Al₂ O₃, SiO₂,or SiO. In the preferred embodiment, the magnetic pillars 21A, 21B ofthe prior art structure shown in FIG. 4(a) are eliminated altogether.Instead, the top magnetic pole-pieces 28A, 28B form magnetic closures27A, 27B, respectively, with both ends of the bottom magnetic layersegment 20. The magnetic closures 27A, 27B are formed in the same or asimilar manner as described earlier to form back-closure 26 in FIG. 2.Alternatively, the planar toroidal TFH may include the two magnetic corepillars 21A, 21B, as shown in FIG. 4(a). In this case, the pillars 21A,21B contact the bottom magnetic segment 20 on either side, and each ofthe top magnetic pole-pieces 28A, 28B contacts one of the two pillars21A, 21B, as shown in FIG. 4(a). Each of the top pole-pieces 28A, 28Bmay have a yoke-arm shape, as shown in FIGS. 3(b) and 4(a). Each topmagnetic pole-piece segment 28A, 28B includes an elongated portion, afan-like portion (or flux concentrator), and a pole-tip. In thepreferred embodiment, the elongated portion comprises a constant width,which is essentially equal to the width of the bottom magnetic layersegment 20. In another embodiment (not shown), the elongated portion mayhave a tapered shape, where the magnetic closure is wider than the widthat the onset of the fan-like portion. Pole-tips 30A, 30B may consist ofan additional layer formed on top of the pole-pieces 28A, 28B, as shownin FIG. 4(a), or they may be integral portions of the pole-pieces 28A,28B formed in a single layer, as shown in FIG. 4(b). Insulation layers19, 25, 37, 38, 40, and 41 are formed in the same or similar manner asdescribed above in conjunction with the structure shown in FIGS.1A-3(d). Similarly, coil layers 32B, 36A, and 36B are formed in the sameor similar manner as described above in conjunction with FIGS. 1A-3(d).At least one turn of a toroidal solenoid winding is wrapped around atleast one segment or pillar of the magnetic core. Transducing gap 24 isformed over insulating pedestal 44 in a manner well known in the art ofplanar TFH devices. FIG. 4(b) shows an embodiment where the pole-tips30A, 30B are integral parts of the top magnetic pole-pieces 28A, 28B,formed in a single layer. In the embodiment of FIG. 4(b) insulatingpedestal 44 is formed over insulation layer 40 prior to the depositionof the top magnetic pole-pieces 28A, 28B. In another embodiment, thepole-tips 30A, 30B are formed in a separate layer. In this embodiment,the top magnetic pole-pieces 28A, 28B are first formed over insulationlayer 40. Then pedestal 44 is formed over insulation 40 between thepole-pieces. Finally, pole-tips 30A, 30B are formed over both thepole-pieces and the pedestal, as shown in FIG. 4(a). The planar toroidalhead of FIG. 4(b) can be embedded in an insulation material 45, whichmay comprise alumina, silicon dioxide, or other commonly used ceramics.In the embodiment where insulating layer 41 comprises Al₂ O₃, SiO₂, orSiO, layer 41 may extend to the ABS, as shown in FIG. 4(b). However, inthe embodiment where layer 41 comprises a hard-baked photoresist orcured polyimide, it must terminate below the ABS level, in order toavoid the material of layer 41 smearing over the pole-tips duringstart-stop operations. Upon completion of fabricating the top coil layer36B, excess insulation layer 45 is deposited over the entire wafer anddevices. This layer is then lapped-down to expose pole-tips 30A, 30B andthereby to define the air bearing surface, ABS, and the throat height(the height of gap 24 defined as the depth of the gap which is thedistance from the ABS to point 24A). Slider rails (not shown) are thenformed in the ABS of layer 45 by well-known photolithographic definitionand etching (by wet chemical etching, ion milling, or reactive ionmilling). This is done at the wafer level, simultaneously for all thedevices on the wafer. Finally, completed individual sliders are dicedfrom the wafer, with no further rail machining and/or throat lapping.

Other embodiments of the planar toroidal TFH device may be fabricated.For example, rather than a symmetrical position of gap 24 relative tothe head, the gap may be located at other asymmetric positions along thetop magnetic pole-pieces. Additionally, in the embodiment which employsmagnetic pillars (such as pillars 21A, 21B, (FIG. 4(a))) in the core,solenoid toroidal windings may also be included around the magneticpillars, thereby improving the magnetic coupling efficiency of the coilto the core.

In another embodiment, the planar toroidal TFH is built in a cavityformed in a flat surface of the substrate. The method of forming theplanar toroidal head at the bottom of the cavity follows the same stepsas those described above. At the end of the construction of the device,the device is buried under, and the cavity is filled with, ceramicmaterial such as Al₂ O₃, SiO₂, or SiO. The final lapping forms a smoothsurface on the substrate material and adjusts the throat height of thehead to its final dimension. Flying rails or other ABS patterns are thenformed in the ceramic layer, before the sliders are cut apart.

FIGS. 5(a) and 5(b) illustrate prior art conventional spiral coilinductive write elements in "merged" magnetoresistive (MR) heads. FIG.5(a) is a schematic perspective view of the merged MR head and FIG. 5(b)is a longitudinal cross-section of the same head. The basic structureconsists of a substrate 48 (which may include an undercoat layer such asalumina) upon which is formed the bottom magnetic shield 49 for the MRread sensor 50. Combined layers 51 constitute the read gap. Layer 51electrically insulate the MR sensor from its magnetic shields. Region 52is used for electrical connections to the MR sensor as well as formagnetic biasing. Layer 53 serves as both the top magnetic shield forthe MR sensor and the bottom pole (P1) for the inductive write element.Because of this shared dual function, the head is called a "merged" MRhead. Layer 54 is the write gap of the inductive TFH. It usuallycomprises an insulating material such as Al₂ O₃, SiO₂, or SiO. Flatspiral conducting coil winding 55 carries the write current. The coilleads are connected to the write drive at terminal pads 56 and 57.Electrical connection to the central end of coil 55 is made through via58. Top pole (P2) 59 forms a back magnetic connection to bottom pole(P1) 53 through a via 60. Pole tip 61 of the inductive write elementdefines the width of the written data track. As indicated in FIG. 5(a),MR sensor 50 is somewhat narrower than top pole-tip 61, in order tominimize side reading problems inherent with the MR sensors. Theinductive element in the prior art MR heads cannot be used for readingdue to several reasons. The small number of turns implies too low asignal output, since the signal output is directly related to the numberof coil turns. Also, the much wider bottom pole 53 would pick up datafrom adjacent tracks, as excessive noise. Finally, the storage mediumlayer optimized for MR heads is thinner (or lower M_(r) T) than themedia optimized for inductive heads. This further reduces the signaloutput read by the inductive element in the prior art MR heads.

FIGS. 6(a) and 6(b) show a perspective view and a longitudinalcross-sectional view, respectively, of a toroidal "merged" MR headaccording to one embodiment of the invention. FIG. 6(b) shows a shorterbottom shield 49 than top shield 53. Functionally, the shields need onlyexceed the length of the MR element 50 by a factor of a few times inorder to adequately shield the MR element from stray fields. Sharedbottom pole (or top shield) 53 must extend to back closure 26 in orderto complete the magnetic circuit of the inductive write element. Thevarious elements of the toroidal MR TFH are constructed utilizingsimilar methods to those described above, as well as prior art methodsrelevant to MR heads. Top pole 59 has a structure similar to the polesdescribed in FIGS. 2, and 3(b) above. Top pole 59 includes a similarback closure region 26 which minimizes magnetic noise, as previouslydescribed. Coil 36 comprises a solenoid toroidal winding, rather than aflat spiral structure. In the embodiment shown in FIGS. 6(a) and 6(b),the coil is wrapped around only the top pole. In other embodiments thecoil may be wrapped around the bottom pole or around both poles. Inembodiments which do not require the inductive write element to alsoread servo and/or track data, the number of coil turns should beminimized in order to reduce inductance and resistance. In one suchembodiment, the toroidal coil may comprise a single turn. In thisembobiment, the width of the single turn occupies almost the entirespace between the pole-tip 61 and back closure 26. The length ofmagnetic poles 53 and 59 of a single-turn toroidal MR device may besignificantly shorter than that required for a multi-turn coil device.The shorter (and narrower) pole dimensions offer the further advantageof reduced device inductance. The single toroidal turn may be wrappedaround either the top yoke-arm or the bottom yoke-arm. In anotherembodiment, one single toroidal turn is wrapped around the top yoke-armand an additional toroidal turn is wrapped around the bottom yoke-arm.The toroidal MR device may similarly include other small number oftoroidal turns wrapped around either or both of the magnetic poles. Thewrite function of the "merged" MR head is significantly improved by theincorporation of the toroidal structure. Because of the significantlylower inductance, the shape and rise time of the write pulse is greatlyimproved (shorter rise time). In addition, the resonance frequency ofthe write head is significantly expanded, allowing much higher datatransfer rates.

FIG. 7(a) shows an embodiment of a "merged" toroidal MR head where thesolenoid toroidal coil is wrapped around both poles. In this embodiment,the total number of turns may be more than three times that of aconventional MR write element, yet maintaining lower coil resistance,inductance, and capacitance. These enable very low noise and very hightransfer rates. The inductive toroidal element of this embodiment issimilar to the one described in FIG. 2, except that the coil turns 32wrapped around bottom pole 53 do not cover the entire length of thispole but rather only extend to a depth near the end of bottom shield 49.Bottom shield 49 only needs to extend away from the ABS to a depth whichis several times larger than the depth of the MR element. Thus the depthof bottom shield 49 need only extend to a depth of about 3-15 μm fromthe ABS.

Due to its larger number of coil turns, this toroidal write element isalso capable of reading servo and/or data tracks. While small radii datatracks are best read by the MR read element, the larger radii tracks(having larger tangential velocity) can be read by the toroidal element.Thus the total performance of the head may be significantly improvedover that of the conventional MR head. In order for the inductivetoroidal element to read properly, the width of the bottom pole-tipshould be similar to that of the top pole-tip. The prior art "merged" MRhead of FIG. 5(a) employs much wider bottom pole-tip than the toppole-tip. Such a configuration is, therefore, inadequate for readingwith the toroidal element. FIG. 7(b) illustrates schematically thepole-tip's configuration according to one embodiment of the invention.Shared bottom pole and top shield 53 is partially etched in regions 63to form an elevation 62 having a width essentially the same as that ofthe top pole-tip 61. The etching can be carried out by a self-alignedpole-trimming method, such as described in U.S. Pat. Nos. 5,141,623 and5,200,056, incorporated herein by reference, or by any other suitabletechnique. The depth of the etching of elevation 62 should not exceedmore than about one half of the original thickness of pole/shield 53.Preferably this elevation should be in the range between about 0.5 μm to1.5 μm. In the pole-trimming process of U.S. Pat. Nos. 5,141,623 and5,200,056 the etched regions 63 automatically extend from the ABS adistance equal to the throat height, which is shown and defined aslength 22 in FIG. 2. However, the etched regions 63 may also extend fromthe ABS to a shorter, or to a longer distance than the throat height.For example, the etched region may be extended past the end of thethroat, along dashed line 64 to create elevation with a spreading fanshape, similar to that of the top pole.

The improvements embodied in the "merged" toroidal MR head facilitatewriting at very high data rates, plus the ability to read servo dataand/or data tracks with the inductive toroidal element. Since MRelements are flux sensors, they work even when the magnetic media movesrelatively slowly relative to the head. Inductive heads, on the otherhand, sense the rate of change of the flux, and therefore perform betterat higher velocities. While the signal to noise ratio (SNR) of theinductive element improves with disk velocity, that of the MR elementdoes not. In fact, for a given linear density along the track, the SNRof an MR element actually drops with increasing disk velocity due to theincreased frequency and associated thermal noise. Thus, for optimumperformance it would be advantageous to use the MR element to read datastored at small radii near the inner diameter (ID) of a spinning disk,where the tangential velocities are relatively low. It would also beadvantageous to use the inductive toroidal element to read data storedat larger radii tracks, near the outer diameter (OD), where tangentvelocities are higher. By combining the inductive toroidal element ofthis invention with a shielded MR element in the same device, optimizedperformance can be realized.

FIG. 8 shows another embodiment of the invention which combines aninductive toroidal element with an MR sensor. This is the "combination"or "composite" version of the toroidal MR TFH device. In thisembodiment, the magnetic shields 49, 53(b) of the MR element arecompletely separate from the inductive toroidal element (no shared topshield/bottom pole). The inductive toroidal element is similar to theone described in FIG. 7(a). Shields 49 and 53B only need to extend ashort depth (about 3-15 μm) from the ABS. Insulation layer 65 separatesthe MR element 50 from the inductive toroidal element which includesmagnetic poles 53, 59 and toroidal coils 32A, 32B, 36A and 36B. Layer 65should be relatively thin, in order to minimize offset between inductivetoroidal element and MR sensor 50. This offset is related to the skewangle between the slider and the storage track, which varies with thetrack diameter. On the other hand, insulation layer 65 should be thickenough to prevent electrical and magnetic interference between the twoelements. Layer 65 may have a thickness ranging from about 100 Å toabout 5 μm and may comprise Al₂ O₃, SiO₂, SiO, or any other non-magneticinsulating material.

Other embodiments of the invention also include an inductive toroidalwrite element and a separate read element. The read element may consistof either an MR element or another toroidal inductive element. In oneembodiment, the separate elements are situated one on top of the other.In this embodiment, magnetic shields, such as shields 49 and 53 in FIG.7(a) and shields 49 and 53B in FIG. 8 are required. In anotherembodiment, the separate elements are situated side-by-side on the samerail. In another embodiment, the separate elements are situated each ona separate rail of the slider. In yet another embodiment, at least onepair of separate elements (each pair consisting of an inductive toroidalelement and a read element such as an MR sensor or another inductivetoroidal element) is situated on each rail of the slider.

In other embodiments of the invention, the inductive toroidal elementmay be combined with a pinched-gap TFH device. The pinched-gap TFHstructures and methods for its manufacture are described in pendingapplication Ser. Nos. 07/963,783, 08/315,810, and 08/477,011, and in apublication entitled "A Pinched-Gap Magnetic Recording Thin Film Head",Paper #233, The Electrochem. Soc. Conf., Oct. 10-15, 1993, and in the3rd Int. Symp. on Magnetic Materials, Processes and Devices, edited byL. T. Romankiw and D. A. Herman, The Electrochemical Society, NJ (1994),incorporated herein by reference. In one embodiment of this invention, asingle read/write inductive toroidal element (or head) is combined withpole-tips having the pinched-gap configuration. In another embodiment ofthis invention, an inductive toroidal write element, which comprisespole-tips having the pinched-gap configuration, is combined with aseparate optimized read element. The optimized read element may comprisea separate inductive toroidal element with conventional (no pinched-gap)pole-tips configuration, or it may comprise an MR element. Oneparticular combination is a toroidal inductive write element with a"merged" MR read element, where the bottom pole of the toroidalinductive write element is merged (or shared) with the top magneticshield, its shown in FIGS. 7(a) and 7(b), but where the pole-tips of thewrite element have a pinched-gap configuration (not shown). Anotherembodiment, similar to FIG. 8, comprises an inductive toroidal element,having a pinched-gap pole-tips configuration (not shown), combined withan MR element having separate shields.

While the invention has been particularly described with reference topreferred embodiments, it will be understood by those skilled in the artthat various changes in form and detail may be made therein withoutdeparting from the spirit, scope, and teaching of the invention.Accordingly, examples herein disclosed are to be considered merely asillustrative and the invention to be limited only as specified in theclaims.

What is claimed is:
 1. A toroidal-magnetoresistive (MR) thin film head(TFH) device comprising:a substrate; an inductive toroidal write elementcomprising:a bottom magnetic pole disposed over said substrate andincluding a bottom yoke-arm and a bottom pole-tip portion, said bottomyoke-arm comprising an elongated first back portion of a predeterminedlength and width, said back portion having a first back-end; anon-magnetic gap layer formed over at least said bottom pole-tip portionof said bottom magnetic pole; a top magnetic pole disposed over said gaplayer and substantially overlying said bottom magnetic pole, said topmagnetic pole including a top yoke-arm and a top pole-tip portion, saidtop yoke-arm having an elongated second back portion of a predeterminedlength and width, and a transitioning front portion extending betweensaid second back portion and said top pole-tip portion, said second backportion having a second back-end; said first back portion of said bottomyoke-arm and said second back portion of said top yoke-arm beingmagnetically connected to each other at a back-closure region extendingalong substantially the entire width of at least one of said first andsecond back-ends such that said bottom magnetic pole and said topmagnetic pole combine to form a magnetic core; and at least one solenoidcoil wrapped around at least one of said magnetic poles, said at leastone solenoid coil comprising:a first set of electrically conductivestrips disposed below, and being insulated from, said at least onemagnetic pole; a second set of electrically conductive strips disposedabove, and being insulated from, said at least one magnetic pole; andsaid first set of electrically conductive strips and said second set ofelectrically conductive strips being joined along the sides of said atleast one magnetic pole in a manner to form a solenoid coil wrappedaround said at least one magnetic pole; and a magnetoresistive (MR) readelement.
 2. The toroidal-MR TFH device of claim 1 wherein said at leastone solenoid coil comprises at least one solenoid turn wrapped around atleast one of said magnetic poles.
 3. The toroidal-MR TFH device of claim2 wherein said at least one solenoid coil comprises a single turn. 4.The toroidal-MR TFH device of claim 2 wherein said at least one solenoidcoil comprises a selected number of turns to enable said inductivetoroidal write element to read information stored on a magnetic mediummoving relative to said inductive toroidal write element.
 5. Thetoroidal-MR TFH device of claim 1 wherein said bottom magnetic pole ofsaid inductive toroidal write element also functions as a top magneticshield for the MR read element.
 6. The toroidal-MR TFH device of claim 5wherein said MR read element comprises a bottom shield that is shorterthan said top shield.
 7. The toroidal-MR TFH device of claim 6 whereinsaid at least one solenoid coil comprises multiple turns wrapped aroundboth of said top and said bottom magnetic poles.
 8. The toroidal-MR TFHdevice of claim 6 wherein said bottom magnetic pole of said inductivetoroidal write element is partially etched in said pole-tip portion in amanner such as to form an elevation in said bottom magnetic pole, saidelevation being aligned under said top pole-tip and having a widthessentially equal to the width of said top pole-tip.
 9. The toroidal-MRTFH device of claim 5 wherein said bottom magnetic pole of saidinductive toroidal write element is partially etched in said pole-tipportion in a manner such as to form an elevation in said bottom magneticpole, said elevation being aligned under said top pole-tip and having awidth essentially equal to the width of said top pole-tip.
 10. Thetoroidal MR TFH device of claim 9 wherein the depth of said elevation insaid bottom magnetic pole is between 0.5 μm and 1.5 μm.
 11. Thetoroidal-MR TFH device of claim 5 wherein said at least one solenoidcoil comprises at least one turn wrapped around said bottom magneticpole.
 12. The toroidal-MR TFH device of claim 11 wherein said at leastone solenoid coil comprises a single turn.
 13. The toroidal-MR TFHdevice of claim 12 wherein the width of said single turn occupies mostof the space between said pole-tips and said back-closure region. 14.The toroidal-MNR TFH device of claim 5 wherein said at least onesolenoid coil comprises at least one turn wrapped around said topmagnetic pole.
 15. The toroidal-MR TFH device of claim 14 wherein saidat least one solenoid coil comprises a single turn.
 16. The toroidal-MRTFH device of claim 15 wherein the width of said single turn occupiesmost of the space between said pole-tips and said back-closure region.17. The toroidal-MR TFH device of claim 1 wherein said bottom magneticpole of said inductive toroidal write element is separate from a topmagnetic shield of said MR element.
 18. The toroidal magnetoresistive(MR) thin film head device of claim 17 wherein said at least onesolenoid coil comprises at least one turn wrapped around at least one ofsaid magnetic poles.
 19. The toroidal-MR TFH device of claim 18 whereinsaid at least one solenoid coil comprises a single turn wrapped aroundeither said bottom magnetic pole or said top magnetic pole.
 20. Thetoroidal-MR TFH device of claim 19 wherein the width of said single turnoccupies most of the space between said pole-tips and said back-closureregion.
 21. The toroidal-MR TFH device of claim 17 wherein said MR readelement comprises a bottom shield that is shorter than said top shield.22. The toroidal-MR TFH device of claim 21 wherein said at least onesolenoid coil comprises multiple turns wrapped around both of said topand said bottom magnetic poles.
 23. The toroidal-MR TFH device of claim1 wherein said inductive toroidal write element comprises pole-tipshaving a pinched-gap configuration.
 24. The toroidal-MR TFH device ofclaim 1 wherein said device is disposed on a 30%, or smaller,form-factor slider.
 25. The toroidal-MR TFH device of claim 1 comprisingtwo of said solenoid coils, each of said solenoid coils being wrappedaround a respective one of said top and bottom magnetic poles.
 26. Atoroidal thin film head (TFH) device for transferring information to andfrom a magnetic storage medium, said device comprising:a substrate; aninductive toroidal write element comprising:a bottom magnetic poledisposed over said substrate and including a bottom yoke-arm and abottom pole-tip portion, said bottom yoke-arm comprising an elongatedfirst back portion of a predetermined length and width, said backportion having a first back-end; a non-magnetic gap layer formed over atleast said bottom pole-tip portion of said bottom magnetic pole; a topmagnetic pole disposed over said gap layer and substantially overlyingsaid bottom magnetic pole, said top magnetic pole including a topyoke-arm and a top pole-tip portion, said top yoke-arm having anelongated second back portion of a predetermined length and width, and atransitioning front portion extending between said second back portionand said top pole-tip portion, said second back portion having a secondback-end; said first back portion of said bottom yoke-arm and saidsecond back portion of said top yoke-arm being magnetically connected toeach other at a back-closure region extending along substantially theentire width of at least one of said first and second back-ends suchthat said bottom magnetic pole and said top magnetic pole combine toform a magnetic core; and one or more solenoid coil windings wrappedaround a respective one or more of said magnetic poles, each of said oneor more solenoid coil windings comprising:a first set of electricallyconductive strips disposed below, and being insulated from, each of saidone or more magnetic poles; a second set of electrically conductivestrips disposed above, and being insulated from, each of said one ormore magnetic poles; and said first set of electrically conductivestrips and said second set of electrically conductive strips beingjoined along the sides of each of said one or more magnetic poles in amanner to form a solenoid coil wrapped around each of said one or moremagnetic poles; and a read element comprising a TFH device.
 27. Thetoroidal TFH device of claim 26, wherein said read element comprises amagnetoresistive (MR) device.
 28. The toroidal TFH device of claim 27,wherein said read element and said inductive write element are situatedin tandem with each other.
 29. The toroidal TFH device of claim 27,wherein said read element and said inductive write element are situatedside-by-side on a rail of a slider.
 30. The toroidal TFH device of claim26, wherein said read element and said inductive write element aresituated on different rails of a slider.
 31. The toroidal TFH device ofclaim 26, wherein said read element comprises an inductive toroidal TFHdevice.
 32. The toroidal TFH device of claim 31, wherein said readelement and said inductive write element are situated side-by-side on arail of a slider.
 33. The toroidal TFH device of claim 31, wherein saidread element and said inductive write element are situated on differentrails of a slider.
 34. The toroidal TFH device of claim 26 comprising atleast one pair of an inductive toroidal write element and a read elementplaced side-by-side on a rail of said slider, each of said at one pairbeing situated on a separate rail of said slider.
 35. The toroidal TFHdevice of claim 26 wherein said bottom and top pole-tip portions have apinched-gap configuration.
 36. A thin film head (TFH) devicecomprising:a substrate; a bottom magnetic pole disposed over saidsubstrate and including a bottom yoke-arm and a bottom pole-tip portion,said bottom yoke-arm comprising an elongated first back portion of apredetermined length and width, said first back portion having a firstback-end; a non-magnetic gap layer formed over at least said bottompole-tip portion of said bottom magnetic pole; a top magnetic poledisposed over said gap layer and substantially overlapping said bottommagnetic pole, said top magnetic pole including a top yoke-arm and a toppole-tip portion, said top yoke-arm having an elongated second backportion of a predetermined length and width, and a transitioning frontportion extending between said second back portion and said top pole-tipportion, said width of said second back portion being not greater thansaid width of said first back portion of said bottom yoke-arm, saidsecond back portion having a second back-end; said first back portion ofsaid bottom yoke-arm and said second back portion of said top yoke-armbeing magnetically connected to each other at a back-closure regionextending along substantially the entire width of said second back-endsuch that said bottom magnetic pole and said top magnetic pole combineto form a magnetic core; and at least one solenoid coil winding,comprising at least one turn, wrapped around at least one of saidmagnetic poles, for each of said at least one magnetic pole beingwrapped by a solenoid coil, said solenoid coil winding comprising:afirst set of electrically conductive strips disposed below, and beinginsulated from, said magnetic pole; a second set of electricallyconductive strips disposed above, and being insulated from, saidmagnetic pole; said first set of electrically conductive strips mindsaid second set of electrically conductive strips being joined along thesides of said magnetic pole in a manner to form a solenoid coil wrappedaround said magnetic pole.